Share-Based Compensation Arrangements (Share Options Activity) (Details) - Stock Options [Member] - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Number of Share Options:
Beginning of period	219,279
Granted	47,725	53,400	48,600
Exercised	(39,076)
Forfeited or expired	(4,075)
End of period	223,853	219,279
Options exercisable	80,003
Options expected to vest in future periods	143,850
Weighted Average Exercise Price (in dollars per share):
Beginning of period	$ 32.70
Granted	58.05
Exercised	28.30
Forfeited or expired	43.06
End of period	38.68	$ 32.70
Options exercisable	25.89
Options expected to vest in future periods	$ 45.80
Outstanding Weighted Average Remaining Contractual Term	7 years 2 months 20 days
Exercisable Weighted Average Remaining Contractual Term	4 years 4 months 18 days
Expected to Vest Weighted Average Remaining Contractual Term	8 years 9 months 18 days
Outstanding Aggregate Intrinsic Value	$ 3,487
Exercisable Aggregate Intrinsic Value	2,189
Expected to Vest Aggregate Intrinsic Value	$ 1,298